1. Field of the Invention
The present invention relates to a camera having a plurality of mechanisms driven by an electric motor which is rotatable in both the forward and backward directions, including a lens barrel driving mechanism for performing a drive of extension and collapse of a lens barrel.
2. Description of the Related Art
Hitherto, there are known many types of cameras provided with various mechanisms, for example, a mechanism for performing a drive of extension and collapse of a lens barrel, a focusing mechanism, a film feed mechanism, a film development discharge mechanism in an instant camera and so on. Of the cameras incorporating those mechanisms, there is a camera having such an arrangement that an electric motor is included and those mechanisms are driven by the motor.
As to a camera having such an electric motor, hitherto, in order to reduce the number of motors, there is known such a technical concept that a direction of a rotation of a single electric motor is changed on a switching basis so that the respective mechanisms are driven by the same motor. For example, according to the Japanese Utility Model Registration No. 1869801, there is known such a technology that a single electric motor is used so that a selection mechanism for wide-angle/telephoto of barrel is performed by rotation of the electric motor in a certain direction, and another mechanism, for example, a film feed mechanism or a shutter mechanism, is driven by rotation of the electric motor in a reverse direction.
Further, Japanese Patent Laid Open Gazette Hei. 9-236854 discloses a technology that a single electric motor is used so that a film feed, a film wide and a film rewind are performed by rotation of the electric motor in a certain direction, and another mechanism is driven by rotation of the electric motor in a reverse direction.
The technical concepts disclosed in the above-mentioned publications are to drive different mechanisms in accordance with a direction of a rotation. However, the above-mentioned publications simply propose objects to be driven by a single electric motor, for example, in such a way that a lens mechanism or a film feed mechanism is driven in a certain direction of a rotation, and fails to suggest any solution for problems involved in practical use of the switching driving mechanism.
For example, in the event that different mechanisms are driven in accordance with a forward rotation and a reverse rotation of an electric motor, it is general that a planetary mechanism for switching a transmission of a rotary driving force of the electric motor between those mechanisms. Further, in some schemes of extension and collapse of a lens barrel, there is provided a screw barrel in which extension and collapse of a lens barrel are performed on a rotational transfer basis. In the event that a lens barrel having such a screw barrel is provided, and a planetary mechanism is disposed in such a manner that when a single motor is rotated forward, the lens barrel is driven, and when the motor is rotated reversely, another mechanism is driven, when the electric motor is reversely rotated after the electric motor is rotated forward so that the lens barrel is extended, there is offered such a state that an engagement between the planetary mechanism and the mechanism for driving the lens barrel is released while the lens barrel is kept on extension. This causes a situation that simply touch on the screw barrel by a finger permits a rotation of the screw barrel, so that an extension position of the lens barrel is out of the proper position. Thus, there is a possibility that a photography involving no suitable focusing is performed.
This is the same also in the even that the electric motor is stopped without being reversely rotated, after the electric motor is forwardly rotated to extend the lens barrel. When an external force is applied to the screw barrel in a direction wherein the electric motor is reversely rotated, an engagement between the planetary mechanism and the mechanism for driving the lens barrel is relatively easily released. Thus, this causes the same problem as the event that the motor is reversely rotated.